My Last Sigh wrote:
I am reading a book on studio tricks used to create bigger
sounds in
home recording. One term mentioned is to dupe a track,
and "flip the
phase" of the track.

A *BAD* choice of words, even though we all know it is quite
customary.

While I know what this means technically,

It means flipping the polarity of the signal.

what does one do to "flip the phase" on a digital
recording?

You flip the polarity of the signal. There's usually a
pushbutton or an effect that does this, someplace in the
software, device driver, or whatever.

Is there a piece of hardware to use, or should I try
software, or what?

The facility for changing polarity of a channel is where you
find it. It's in some device drivers, and its a standard
effect in most DAW software.

Note that flipping the polarity is really quite different
from 180 degrees of phase shift. 180 degrees of phase shift
implies a time delay, while flipping polarity does not.